Not applicable.
I. Field of the Invention
The present invention relates to a system for controlling a printing machine capable of producing single-sided (simplex) and double-sided (duplex) prints for monochrome or color or mixed monochrome or color to create personalized collated sets containing variable data, as for example, bills, invoices, proposals with personalized cover letters, insurance policies, direct marketing materials etc., with very high productivity.
On-demand page printers, wherein images are created in response to digital image data submitted to the printing apparatus, are familiar in many offices. Such printers create images on sheets typically using electrostatographic or ink-jet printing techniques. In work-group situations, wherein different users at various personal computers and other terminals submit jobs to a single central printing apparatus, various sets of digital image data, corresponding to jobs desired to be printed by different users, are typically kept in an electronic queue, and a control system typically located at the printer sorts through the image data and causes the printer to output the desired prints in an orderly manner.
Particularly with sophisticated printing apparatus, it may often be desired to print xe2x80x9cduplexxe2x80x9d prints, that is prints having images on both sides of the sheet. However, most currently available printing devices are capable of producing an image only on one side of a sheet at a time. In order to obtain duplex prints, it is almost always necessary to provide an xe2x80x9cinverterxe2x80x9d within the printing device or apparatus. The purpose of an inverter is to handle a sheet after one side thereof has received an image, and in effect turn the sheet over to make the remaining blank side available to the same printing apparatus which created the first image. In effect, each duplex print is re-fed past the image-making portion of the printing apparatus so that the individual sheet becomes available to the image-making apparatus twice, once for each side.
A long-standing concern of designers of a printing apparatus is how to optimize the use of a printing apparatus for situations wherein some desired prints are simplex and others are duplex as well as some being monochrome and others being color while the number of personalized sets are small (usually one). The fact that each duplex print has to be printed essentially twice and color print may have to be printed multiple times, causes a significant systemic problem with maintaining optimal or near-optimal operation of the entire printing apparatus.
II. Description of the Prior Art
In an electrostatographiic printing apparatus, wherein images are first created on a photoreceptor in the form of a rotating drum or belt and then transferred to sheets, a key concern is the presence of blank pitches (image-sized spaces) along the drum or belt where, for various reasons relating to intermixed simplex or duplex jobs, when no image is created. The problem with blank pitches is that each blank pitch represents lost productivity. In some duplexing and or multi-pass color printing schemes, the number of blank pitches along the belt may be comparable to the number of pitches actually having images on them. In such a situation, not only is the apparatus effectively running at half-speed, but various mechanical parts associated with the drum or belt will be experiencing wear to no productive purpose. Thus, as a general rule, the overall productivity and reliability of such a printing apparatus is inversely related to the number of blank pitches which result in the printing process.
One simple solution, for example intermixed (simplex only) color and monochrome, would be to run every sheet as a color sheet, regardless of whether it is a monochrome or color print, and in the case of each black and white print simply to print nothing on the other transfer cycles. Similarly, for intermixed simplex and duplex jobs, for example, one solution involves running every sheet along the duplex path, regardless of whether it is a simplex or duplex print; and in the case of each simplex print, simply to print nothing on the back side. While this solution is easy to implement, it provides the disadvantages of unnecessarily decreasing the through-put of the whole system.
Another partial solution is to maintain duplex prints which are awaiting printing on the back sides thereof in a special buffer tray, until the system becomes available for printing the back sides of each sheet in sequence. The key disadvantage of this system is that for personalized printing, where the number of identical sets required is one or two, the productivity will be very low due to the idle time while printer is waiting for the one-sided images to settle in the duplex buffer tray. Secondly, significant probability of error exists (a sheet may have the incorrect back side image placed thereon), and also the relatively intense handling of each print sheet in and out of the buffer tray substantially increases a likelihood of mechanical misfeed. Both such problems tend to result from the fact that sheets typically cannot be fed out of the buffer tray reliably. Even with a buffer tray, a fairly sophisticated scheduling system is required.
In the prior art, certain patents assigned to the Xerox Corporation (U.S. Pat. Nos. 5,337,135 and 5,184,185), which are hereby incorporated by reference, have generally dealt with the problem of scheduling sheet s in an imaging system having an endless duplex paper path loop. In general, these various patents disclose different techniques for overcoming the simplex-duplex problem in an electrophotographic printing apparatus. Such techniques include simply finding blank pitches and using them as needed to print simplex prints or cycling down the printer between jobs where a finishing activity, such as stapling, requires an extraordinarily long period of time. Another technique involves causing sheets to move through the system at variable speeds. U.S. Pat. Nos. 5,504,468 and 5,557,367 also assigned to the Xerox Corporation, posits a system in which an optimized schedule for imaging sheets, given the knowledge of the desired output at a given time, is dynamically created in advance in the course of the printing process.
In the case of a conventional two-sided image forming apparatus having a digital scanner and document feeder, copying operations for mixed jobs containing two-sided or single-sided monochrome images are carried out in the manner discussed below.
In order to print a single set of variable print documents, as for example, billing statements, where the number of originals are few and the number of customers are large, the complete print job is treated as one large job with all customer originals accumulated sequentially. The controller automatically checks whether they are one-sided or two-sided images. If one of the pages is two-sided, then, the controller automatically selects the automatic two-sided mode for the whole job. After that, a copy start command is given to the apparatus. The controller prints odd-sided images first in sequence until the duplex loop is filled up followed by the even sided images on the back and then exiting them to the output tray. Printing odd sided images is then resumed, and so on, until the entire job is completed. In this mode of operation, should a toner image representative of a one-sided blank image be transferred to the paper in the same manner as a toner image of a two-sided document, the productivity rate (copying rate) would be critically affected although paper sheets would be discharged in order of page despite the mixture of two different kinds of images. Therefore, the printing operation for the personalized sets of mixed originals where the copying run length is very small (1 or 2 sets), is very inefficient. Also, if the number of sheets in personalized sets is small, as in the case of printing invoices and bills, the productivity losses due to the wait in the duplex loop is significant even if the particular print job involves only duplex copies without any mixed originals.
In situations where personalized mixed printing jobs include color and monochrome, one-sided and two-sided images with variable-data on each page are continuously printed with the image forming apparatus. In such situations generally the printer controller will automatically sort the images into monochrome and color pages, separately print the color pages first, and then run the job in the monochrome mode under a complicated job-programming mode such that previously printed color sheets are also fed into the machine at the proper time under controller command. This operation is very cumbersome and inefficient due to the manual intervention required by the operator to load the pre-printed color sheets for the second pass operation.
Another problem associated with the prior art printing and/or collation devices is that the integrity of the entire print job can be seriously affected due to operator error or to machine multi-feed error. To maintain the set integrity during duplexing, U.S. Pat. No. 5,488,458, dated Jan. 30, 1996, and assigned to the Xerox Corporation, selectively prints solid marks spaced along the sheet on both sides and then reads them with two optical sensors on each side to determine if the corresponding images on both sides have been printed correctly.
It is therefore an object of the present invention to provide a very productive copier, laser printer, or similar image forming apparatus that may contain personalized information on each page being printed. This invention allows discharging of paper sheets in order of page rapidly in any of various copy or print modes which are practicable with a mixed stack of black and white images and color images, both one-sided and two-sided, to create individual sets. It is another object of the present invention to provide a job integrity auditing system for each finished set while the printing job is in process.
The image forming apparatus assumes a supply means to supply the images, which has a built-in or programmed discrimination means to discriminate whether the document pages are one-sided or two-sided, and also to discriminate whether the pages are black and white or color. Then the image forming apparatus selectively outputs copy sheets in either a one-sided copy mode, two-sided copy mode, or mixed-sided copy mode.
This invention is an improvement over my earlier patent, U.S. Pat. No. 5,655,208, involving an apparatus adaptable to execute this process; in particular, for situations when the number of identical sets to be printed for each customer are small (usually one, two, or three).
A preferred feature of this invention is to provide an efficient method for printing short runs of personalized images with variable-data (as for example, single set of invoices, bills, proposals, and reports for each client) containing a mix of single-sided and two-sided black and white or color pages by making a single copy of the said images in a sequence until the number of sheets is equal to the duplex loop length and which is equal to the minimum number of sorter bins. In this regard single image printing of the documents is first performed (as a first succession or mode) until the two-sided paper path loop is filled. This is followed by the printing of the other side of a two-sided copy (as a second succession or mode) after which these printed copies are sent into intermediate sorter bins, whose number is determined by the maximum number of copy sheets in the two-sided copy loop.
Another preferred feature of this invention to provide a method for insuring job integrity of each completed set, in combination with my new and unique process, by tracking the print copy and matching the entry of such copies into the intermediate sorter bins.